Generally, a tonewheel is a component which is mounted to a rotary object so as to sense the rotating speed of the object, such as a drive shaft or a wheel.
For example, FIG. 1 shows a tonewheel 70 which is mounted to a hub 1 of a wheel of a vehicle so as to sense the rotating speed of the wheel.
That is, the tonewheel 70 is press-fitted into the hub 1 of the wheel, and is constructed as shown in FIGS. 2 and 3. Referring to the drawings, the tonewheel 70 includes a boss 71, a sensing part 75, and a coupling part 77. The boss 71 has a cylindrical shape, and is fitted into the hub 1. A plurality of sensing holes 73 is formed along the circumference of the sensing part 75 at regular intervals, thus forming an uneven surface. The coupling part 77 couples the boss 71 to the sensing part 75. Such a tonewheel has the shape of a multi-stage cylinder.
As shown in FIG. 1, a tonewheel sensor 20 is mounted to a position around the tonewheel 70. The tonewheel sensor 20 senses the pulse generated by the sensing holes 73 of the sensing part 75 when the tonewheel 70 rotates along with the rotary object.
Further, a controller mounted on a vehicle analyses the pulse transmitted from the tonewheel sensor 20, thus allowing the rotating speed of the wheel to be checked in real time.
The tonewheel 70, the tonewheel sensor 20, and the controller are used as essential components of an ABS (Anti-Lock Brake System), a TCS (Traction Control System), or a VDC (Vehicle Dynamic Control System).
Thus, the tonewheel 70 must precisely check the rotating speed of the rotary object, such as a wheel, in real time. To this end, the sensing part 75 sensed by the tonewheel sensor 20 must have very precise flatness and a uniform sectional thickness. Further, the uniformity of the shapes and intervals of the sensing holes 73 must be very high.
Unless the flatness of the sensing part 75 is precise and the sectional thickness is uniform, the uniformity of the shapes and intervals of the sensing holes 73 is lowered. This undesirably increases the defect rate of the tonewheel 70.